In process- and automation-technology, frequently, measuring devices are used for determining and/or monitoring process variables. If the medium or the process to be monitored is located in an explosion-endangered region, then, often, galvanic isolation is required, in order to isolate the medium-contacting part of the measuring device in an explosion-endangered region (which is, most often, the process to be monitored, at least with the help of the measuring device), for example, from the energy supply part or from the servicing by operating personnel. For such purpose, measuring devices have, most often, two electronic units, between which such galvanic isolation is provided. Over this isolation, usually the necessary energy for operating the sensor unit is transmitted and also data, e.g. measurement data, wherein data is, on occasion, even transmitted in both directions. In the state of the art, there exists, for this, already a number of known options; see e.g. DE 2 321 900, EP 0 977 406 A1 or EP 0 927 982 B1. These options are, however, very complicated and costly. Another possibility is to transmit the required energy via a transformer as transfer agent and the data via opto-couplers, wherein units are provided on each side of the galvanic isolation, in order to enable bidirectional data transmission. Such a “safe isolation” consumes much space, and, because of the increased component requirements, is also expensive.